We have a node marked as private, which makes it disappear from the node tree. So we grant "can view node" to the registered usergroup so that they can see the node in the tree (and thus know that it exists), but can't see the content.
Later on, a user is granted access to that node. He posts some things. Then his access is revoked.
There's no permission for "can view own threads/posts", so when he clicks on the node, he only sees his own content, and doesn't understand what has gone wrong.
Really, it seems like the better solution would be to add a secondary permission/qualifier for "Private Node" to show the node in the node list regardless. That would fix the need to override the "can view node" permission on a usergroup basis, and I can't imagine a useful reason to have a "can view own threads/posts" permission.